Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 20 Mar 2018 18:28:21 +0100 | Subject | Re: [RFT][PATCH v5 7/7] cpuidle: menu: Avoid selecting shallow states with stopped tick |
| |
On Tue, Mar 20, 2018 at 6:15 PM, Doug Smythies <dsmythies@telus.net> wrote: > On 2018.03.20 11:22 Doug Smythies wrote: >> On 2018.03.19 05:47 Thomas Ilsche wrote: >>> On 2018-03-15 23:19, Rafael J. Wysocki wrote: >>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >>>> >>>> If the scheduler tick has been stopped already and the governor >>>> selects a shallow idle state, the CPU can spend a long time in that >>>> state if the selection is based on an inaccurate prediction of idle >>>> time. That effect turns out to be noticeable, so it needs to be >>>> mitigated. >>> >>> What are some common causes for that situation? >>> How could I trigger this for testing? >> >> It appeared quite readily with my simple 100% load >> on one CPU test. Back then (V3) there only 6 patches in the set, >> and before the re-spin there ended up being a patch 7 of 6, which >> made a significant difference in both package power and the >> histograms of times in each idle state. >> >> Reference: >> https://marc.info/?l=linux-pm&m=152075419526696&w=2 > > I made a kernel (4.16-rc5) with only patches 1 to 6 of 7 (V6) > and also with the poll fix. > > I took an old graph: > http://fast.smythies.com/rjwv3pp_100.png > > and removed an obsolete line and added a line from this > kernel: > > http://fast.smythies.com/rjwv6m_100.png > > I also acquired a trace during the test and observe: > > Report: Summary: > > Idle State 0: Total Entries: 699 : PowerNightmares: 0 : Not PN time (seconds): 0.031169 : PN time: 0.000000 : Ratio: 0.000000 > Idle State 1: Total Entries: 3855 : PowerNightmares: 106 : Not PN time (seconds): 0.123759 : PN time: 43.511914 : Ratio: 351.585856 > Idle State 2: Total Entries: 3688 : PowerNightmares: 181 : Not PN time (seconds): 1.303237 : PN time: 63.241424 : Ratio: 48.526418 > Idle State 3: Total Entries: 528 : PowerNightmares: 115 : Not PN time (seconds): 0.276290 : PN time: 44.764111 : Ratio: 162.018571 > > Where "PowerNightmare" is defined as spending excessive time in an idle state, > and arbitrarily defined for my processor as: > > #define THRESHOLD_0 100 /* Idle state 0 PowerNightmare threshold in microseconds */ > #define THRESHOLD_1 1000 /* Idle state 1 PowerNightmare threshold in microseconds */ > #define THRESHOLD_2 2000 /* Idle state 2 PowerNightmare threshold in microseconds */ > #define THRESHOLD_3 4000 /* Idle state 3 PowerNightmare threshold in microseconds */ > > While this trace file was only about 15 megabytes, I have several 10s of gigabytes of trace data for > V4 + poll fix and never see any excessive time spent in any idle state.
Thanks for this work!
I prefer it with patch [7/7]. :-)
| |